Catalytic synthesis of tetrazoles by a silica supported Zn(II) coordination compound containing azide ligand

Abstract

The reaction of Zn(OAc)2∙2H2O with sodium azide and hydrazone ligand (HL = (E)-4-amino-N'-(1-(pyridin-2-yl)ethylidene)benzohydrazide) gave a new neutral mononuclear Zn(II) coordination compound, [Zn(HL)(N3)2] (1). The compound was characterized by several spectroscopic methods and the structure of 1 was determined by single-crystal X-ray analysis. The analyses revealed that compound 1 has free amine functionality on its structure. Therefore, intermolecular interactions in the crystal structure of 1 were studied by Hrishfeld surface analysis. Due to the presence of suitable functional group to bind to the surface suitable supports, compound 1 was supported on propionyl chloride functionalized silica gel and a heterogeneous catalyst (Si-Zn) was synthesized by amidification reaction. The obtained heterogeneous catalyst was characterized by several solid state analyses like FT-IR, DRS, SEM, XRD, EDS, XPS and TGA. Si-Zn was used as catalyst for the synthesis of tetrazoles from the reaction of nitriles and sodium azide. Due to the presence of azide in the structure of compound 1, the obtained catalyst showed high catalytic activity in the synthesis of tetrazoles. The effects of some parameters on the catalytic performance of Si-Zn (like temperature, solvent and substituent on the nitrile) were investigated and the results showed it has good activity and stability in the catalytic production of tetrazoles.